In processing semiconductor wafers, layers are often deposited on the wafer. For instance, during fabrication of some wafers, one or more copper layers are often applied to one side of a wafer (e.g., by electroplating of the front side of the wafer). When plating a wafer with copper, e.g., a layer of Tantalum Nitride is initially deposited using physical vapor deposition (PVD) to act as a barrier. After the barrier layer has been deposited, a seed copper layer is deposited using PVD or CVD. After the seed layer has been deposited, the bulk copper is deposited using PVD, plating or a combination of the two.
When applying the copper on the wafer, a problem often occurs in that the copper becomes applied onto the bevel edge, including the etch exclusion area, and/or the backside of the wafer, which may be undesirable. The presence of the copper onto the bevel edge and the backside of the wafer may cause problems in subsequent fabrication. For instance, during subsequent fabrication, some of the copper in these areas may flake off, thereby causing particulate problems and cross-contamination.
Solutions to this problem have been proposed. For example, in order to prevent deposition from occurring on the backside area of the wafer and the bevel edge area of the wafer (in some situations), a front-side clamping mechanism may be used. This front-side clamping mechanism simply includes a shadow ring. The use of a shadow ring is a simple mechanism to focus and/or direct the ions used in sputtering perpendicular to the wafer surface. Statistically, since this technique is not perfectly shadowing the ion flux, some of these ions eventually are also deposited on the regions of the wafer outside the shadow ring (e.g., the bevel edge or the edge exclusion region).
Another solution to the problem associated with the presence of copper on the bevel edge and/or backside areas is removing the unwanted copper after depositing the layer on the front side. In order to remove the copper that is located on the backside area of the wafer and bevel edge area of the wafer (in some situations) without removing any of the copper layers on the front side of the wafer, the copper on the front side of the wafer must be protected. One method of protecting the front-side (or bevel edge in particular situations) of a wafer is by adding additional lithographic steps to apply a protective resist layer over a portion of the front-side and/or beveled edge of the wafer to prevent the copper layer from being removed during the subsequent removal processes. Once the protection layer has been applied, the unwanted copper may be removed through a variety of well-known removal processes (e.g., by applying a chemistry to the copper, etc.). After the unwanted copper has been removed, then chemical film removal occurs to remove the protective layer (e.g., resist ashing). The use of the additional lithographic step followed by the chemical thin film removal and additional cleaning steps increases the cost, complication, and time to the process of putting a copper layer on the front-side of a wafer. It is desirable to avoid the added costs, complication and time associated with putting a copper layer, or any layer, on a wafer.